1. Field of the Invention
The present invention relates to a communication network system including termination stations and repeaters, and in particular to a transmission method and system for large-capacity and long-distance transmission requiring error correction processing.
2. Description of the Related Art
With the recent vast Increase in data transmission capacity, SONET (Synchronous Optical NETwork) or SDH (Synchronous Digital Hierarchy) has been employed as a basic transmission scheme for a fiber-optic communication system.
In submarine transmission systems, the ITU-T Recommendation G.975. xe2x80x9cForward Error Correction for Submarine Systems,xe2x80x9d specifies a frame structure for transporting STM-16 payloads with FEC (Forward Error Correction).
In land transmission systems, similarly, error-correction techniques come under consideration to meet high-speed data transmission lines. For example, a frame format similar to the above frame structure in submarine transmission systems is proposed for the land transmission systems (see xe2x80x9cA proposed implementation for a digital xe2x80x9cWrapperxe2x80x9d for Och overheadxe2x80x9d, James Ballintine, Lucent Technologies, T1X1.5/99-003 Jan. 12-14, 1999.
According to the frame structure proposed by James Ballintine, a frame is formed by multiplexing sixteen 255-byte subframes, each subframe consisting of a 1-byte overhead (OCh-OH: Optical Channel-Overhead), a 238-byte payload (OCh-PE: Optical Channel-Payload Envelope), and a 16-byte redundant code (FEC: Forward Error Correction). The error correction process (here, parity check) Is performed for each subframe and the calculated value is written into the redundancy check bytes. In other words, the FEC process is applied along the line of its corresponding subframe from the OCh-OH to the OCh-PE.
In submarine transmission systems, each repeater is provided with an optical amplifier and therefore it is not necessary to terminate information of an input optical signal at each repeater.
In land transmission systems, however, an input optical signal is converted into an electric signal and it is necessary to terminate information of an input signal at each repeater In this case, the error-correction function must be terminated at each repeater, resulting in increased amount of hardware in each repeater.
It is an object of the present invention to provide a transmission method and system allowing the amount of hardware to be reduced in a repeater of a transmission system.
It is another object of the present invention to provide a transmission method and system allowing easy termination and insertion of necessary information without increasing in the amount of hardware at a repeater.
According to an aspect of the present invention, a method for transferring a signal from a first termination station to a second termination station through at least one repeater, said signal having a frame structure composed of an overhead portion, a payload portion, and an error-correction code portion, includes the step of; dividing said overhead portion into a selected overhead portion to be used for error correction and a non-selected overhead portion not to be used for error correction; and transferring said signal from said termination site to said other termination site through said at least one repeater.
The first termination station may insert first overhead information to said selected overhead portion of said frame to produce an intermediate signal, perform error-correction encoding of the intermediate signal, insert second overhead information to said non-selected overhead portion of an encoded intermediate signal to produce a transmission signal, and transmit the transmission signal to said second termination station.
The second termination station may receive a signal from said first termination station terminate said non-selected overhead portion of a received signal to produce an intermediate signal, perform error-correction decoding of the intermediate signal, and terminates said selected overhead portion of the intermediate signal to produce received data.
A repeater may receive a signal from said first termination station, terminate said non-selected overhead portion of a received signal to produce an intermediate signal, insert first overhead information to said selected overhead portion of said intermediate signal to produce a transmission signal and transmit the transmission signal to said second termination station.
A repeater may receive a signal from said first termination station, terminate said non-selected overhead portion of a received signal to produce a first intermediate signal, perform error-correction decoding of the first intermediate signal, terminate said selected overhead portion of the first intermediate signal to produce a second intermediate signal, insert first overhead information to a selected overhead portion of said second intermediate signal to produce a third intermediate signal, perform error-correction encoding of the third intermediate signal, insert second overhead information to said non-selected overhead portion of an encoded third intermediate signal to produce a transmission signal, and transmit the transmission signal to said second termination station.
The overhead portion is preferably divided into a selected overhead portion and a non-selected overhead portion depending on a type of each overhead. The overhead portion may be divided into a selected overhead portion and a non-selected overhead portion depending on whether an overhead includes information required for network management.
According to another aspect of the present invention, a transmission method for transmitting a signal from a first termination station to a second termination station through at least one repeater, said signal having a frame structure composed of a plurality of subframes, each of which includes an overhead a payload, and an error-correction code, Includes the steps of: determining whether said overhead is a selected overhead for error correction, depending on a type of said overhead: when said overhead is a selected overhead for error correction, performing an error-correction process using information which includes said overhead; when said overhead is not a selected overhead for error correction, performing said error-correction process using information from which said overhead is removed; and transmitting the signal from said first termination station to said second termination station through said at least one repeater.
According to further another aspect of the present invention, in a system for transferring a signal from a first termination station to a second termination station through a plurality of repeaters, said signal having a frame structure composed of an overhead portion, a payload portion, and an error-correction code portion, the first termination station comprises: a first selected-overhead inserting section for inserting first overhead information to said selected overhead portion of said frame to produce a first intermediate signal; an encoder for performing error-correction encoding of the first intermediate signal; a first non-selected-overhead inserting section for inserting second overhead information to said non-selected overhead portion of an encoded first intermediate signal to produce a first transmission signal; and a first transmitter for transmitting said first transmission signal to said second termination station.
The second termination station comprises; a second receiver for receiving said second transmission signal from said first termination station through said repeaters; a second non-selected-overhead terminator for terminating said non-selected overhead portion of said second transmission signal to produce a third intermediate signal; a decoder for performing error-correction decoding of the third intermediate signal; and a selected-overhead terminator for terminating said selected overhead portion of a decoded third intermediate signal to produce received data.
At least one of said repeaters comprises; a first receiver for receiving said first transmission signal from a previous stage: a first non-selected-overhead terminator for terminating said non-selected overhead portion of a received signal to produce a second intermediate signal; a second selected-overhead inserting section for inserting third first overhead information to said selected overhead portion of said second intermediate signal to produce a second transmission signal: and a second transmitter for transmitting the second transmission signal to a following stage.
At least one of said repeaters comprises: a third receiver for receiving a signal from a previous stage; a third non-selected-overhead terminator for terminating said non-selected overhead portion of a received signal to produce a fourth intermediate signal; a second decoder for performing error-correction decoding of said fourth intermediate signal; a second selected-overhead terminator for terminating said selected overhead portion of said fourth intermediate signal to produce a fifth intermediate signal: a second selected-overhead inserting section for inserting first overhead information to a selected overhead portion of said fifth intermediate signal to produce a sixth intermediate signal; a second encoder for performing error-correction encoding of the sixth intermediate signal; a third non-selected-overhead inserting section for inserting second overhead information to said non-selected overhead portion of an encoded sixth Intermediate signal to produce a third transmission signal; and a third transmitter for transmitting the transmission signal to a following stage.
As described above, since the overhead portion of a frame is divided into the selected overhead portion and the non-selected overhead portion, the non-selected overhead portion such as an overhead for network management can be transferred without error-correction processing. Therefore, easy termination and insertion of the overhead for network management are allowed in each repeater. Further, a repeater without error-correction processing of the non-selected overhead portion can be used, resulting in the reduced amount of hardware in the repeater.